Keeping

Keeping "Cool" at Deep-Sea Vents

Using a novel detector attached to a submarine, a research team led by University of Delaware marine scientists has determined that water chemistry controls the location and distribution of two species of weird worms that inhabit deep-sea hydrothermal vent sites. The study, which is the first to demonstrate through real-time measurements how different chemical compounds control the biology at the vents, is reported in the April 12 edition of the journal Nature.

This chemical detector the "electrochemical analyzer" houses electrode sensors for taking chemical measurements at hydrothermal vents. The wand also is equipped with a thermometer.Photo credit: University of Delaware Graduate College of Marine Studies

The interdisciplinary research team included chemists, biologists, and marine engineers from the UD Graduate College of Marine Studies and the Woods Hole Oceanographic Institution, an Astrobiology Institute Lead Team. Other collaborators included scientists from Rutgers University and Analytical Instrument Systems, Inc. The research was supported by the National Science Foundation, the National Oceanic and Atmospheric Administration’s National Sea Grant College Program, and the National Aeronautics and Space Administration.

UD’s George Luther, a marine chemist, and Craig Cary, a marine biologist, worked with Don Nuzzio, president of Analytical Instrument Systems in Flemington, New Jersey, to develop a chemical detector capable of withstanding the harsh conditions at the vents. Their "electrochemical analyzer" consists of a foot-long wand that houses several needle-like, gold-tipped electrodes, which are coated in super-tough plastic to protect them from heat. The wand, which resembles a large, hand-held hairdrier, is connected to a 3-foot-long, 8-inch-diameter tube that houses the system’s electronics. The tube is mounted to the bottom of the submarine Alvin.

Once attached to one of Alvin’s highly maneuverable arms, the analyzer’s wand can be placed near a vent to instantaneously reveal the ingredients in the sulfur-rich stew rocketing out of the Earth’s crust.

"One of the analyzer’s greatest benefits is its ability to detect a number of sulfur compounds simultaneously, such as iron monosulfide, hydrogen sulfide, thiosulfate, polysulfide, and others," says Luther. "Previous techniques could not identify these compounds, which are the lifeblood of the vents."

Tubeworms have no mouth, eyes, or stomach . Their survival depends on a symbiotic relationship with the billions of bacteria that live inside of them.Photo credit: University of Delaware Graduate College of Marine Studies

During the past two years, the research team tested the analyzer at vent sites in the Gulf of California and in the Pacific Ocean. They examined the microhabitats of two different vent worms: the tubeworm (Riftia pachyptila), which looks like a giant lipstick and can grow to 9 feet tall, and the hairy, 5-inch Pompeii worm (Alvinella pompejana), which currently holds the record as the "hottest" animal on Earth.

The tubeworm lives on the seafloor near hydrothermal vents. It has no eyes, mouth, or stomach. Instead, this worm relies on the billions of bacteria that live inside it to make food. Using the analyzer in a tubeworm colony, the scientists confirmed that this animal resides in waters up to 30 C (86 F), and its bacteria require hydrogen sulfide for survival. If the chemical is not present, the tubeworms die.

Unlike the tubeworm, the Pompeii worm eats helpful microbes. "A fleece of bacteria also occupies this worm’s back," says UD marine biologist Craig Cary. In 1998, Cary and his team confirmed that the Pompeii worm is the most heat-tolerant animal on Earth, capable of surviving nearly boiling water.

The Pompeii worm is the most heat-tolerant animal on Earth, able to survive an environment nearly hot enough to boil water.Photo credit: University of Delaware Graduate College of Marine Studies

"The Pompeii worm forms tube-dwelling colonies on the sides of certain vent chimneys," says Cary. By replacing the analyzer’s hairdrier-like wand with a more slender attachment, the scientists were able to insert the device right into the Pompeii worm’s home. They found that the Pompeii worm resides in much hotter water than the tubeworm, with temperatures fluctuating from 40-90 C (104 – 194 F).

According to Luther, this hot water causes an important chemical reaction critical for the worm’s survival. "The higher temperatures allow for the formation of soluble iron monosulfide, a compound that reduces the toxicity of the hydrogen sulfide in the surrounding water," he notes. "So figuratively speaking, you might say the worm’s hot-water home helps keep it out of ‘hot water.’"

While this research demonstrates how differences in chemical compounds control the unique ecology of vent environments, Luther says the study also may aid astrobiologists.

"The interplay of oxygen, iron, and sulfide compounds in controlling biology in primordial environments on Earth could provide a paradigm for the detection of life on other planets," he says. "Europa, one of Jupiter’s moons, is covered in ice. But recent findings suggest that portions of the ice move, which is strong evidence that liquid water lies beneath it, maintained by hydrothermal vents. If hydrothermal vents exist on Europa, there’s a possibility that ancient microbes could live there, too."